1. Field
One or more aspects relate to crystallization apparatuses, and more particularly, to crystallization apparatuses using sequential lateral solidification (SLS), in which a main optical system is formed so as to be capable of tilting at a predetermined angle with respect to a laser generating device, thereby simultaneously preventing formation of a strain during crystallization or formation of a non-crystallization area.
2. Description of the Related Art
Active matrix (AM) type organic light emitting display apparatuses include a pixel driving circuit in respective pixels. The pixel driving circuit includes a thin film transistor (TFT) formed of silicon. Amorphous silicon or polycrystalline silicon may be used as the silicon constituting the TFT.
In regard to an amorphous silicon TFT (a-Si TFT) used in the pixel driving circuit, since a semiconductor active layer constituting a source, a drain, and a channel is formed of amorphous silicon, the amorphous silicon TFT has low electron mobility. Thus, a polycrystalline silicon TFT instead of the amorphous silicon TFT is now being used. The polycrystalline silicon TFT has high electron mobility and superior light irradiation stability compared to the amorphous silicon TFT. Thus, the polycrystalline silicon TFT is very suitable for use as an active layer of a driving and/or switching TFT of an active matrix organic light emitting display apparatus.
The polycrystalline silicon TFT may be manufactured using various methods. The various methods may be largely classified into a method in which polycrystalline silicon is directly deposited and a method in which amorphous silicon is deposited and crystallizing the deposited amorphous silicon. The method for depositing the polycrystalline silicon may include a chemical vapor deposition (CVD) method, a photo CVD method, a hydrogen radical (HR) CVD method, an electron cyclotron resonance (ECR) CVD method, a plasma enhanced (PE) CVD method, or a low pressure (LP) CVD method.
The method in which the amorphous silicon is deposited and the deposited amorphous silicon is crystallized may include a solid phase crystallization (SPC) method, an excimer laser crystallization (ELC) method, a metal induced crystallization (MIC) method, a metal induced lateral crystallization (MILC) method, or a sequential lateral solidification (SLS) method.
The SPC method is not very practical since it needs to be performed at a temperature greater than about 600° C. for a long period of time. The ELC method may realize low-temperature crystallization. However, since a laser beam is expanded using an optical unit, uniformity may be deteriorated. Meanwhile, the MIC method has a low crystallization temperature since a metal thin film is deposited on a surface of amorphous silicon and a silicon layer is crystallized by using the metal thin film as a crystallization catalyst. However, since polycrystalline silicon is contaminated by the metal, characteristics of a TFT device including a silicon layer may be deteriorated. Also, formed crystals may have a small size and the crystals may be distributed in a disorderly manner.
The SLS method uses the fact that grains of silicon grow in a direction perpendicular to a border surface between liquid-state silicon and solid-state silicon, where a-Si is crystallized by partially melting a-Si by irradiating a laser beam through a particular portion of the a-Si by using a mask and growing crystals from the border between the melted portion and an un-melted portion, in a direction toward the melted portion. The SLS is receiving attention as a method of fabricating low temperature poly-Si.